The present invention relates to apparatus and methods for adjusting the NOX level of emissions of heavy-duty gas turbines for emissions compliance without disassembly of the combustors and particularly relates to a mechanical arrangement enabling external access to the dilution air sleeves for the combustion chamber for adjusting the combustor dilution air flow hole areas and methods of adjustment.
Heavy-duty gas turbines employing dry low NOX, combustion systems are typically installed with predetermined dilution flow hole areas for flowing compressor discharge air into the combustion liner to shape the gas temperature profile exiting the combustion system and provide reduced NOX emissions. Dilution air flow sleeves are typically provided and have a predetermined hole area for flowing compressor discharge air into the combustion liner. Not infrequently, however, and after installation of the turbine at the power generation site, the NOX emissions level is either too high or too low, with corresponding CO emissions level that is too high. This is a result of the normal variability of machine air flow fraction that is delivered to the combustor and the resulting variability of flame temperature in the NOX, producing zones of the combustor.
Under those circumstances, the turbine is typically brought into NOX emissions compliance by removal of the combustion liners from the turbine and resizing the dilution holes to redistribute the combustor air flow. This procedure requires the physical removal of the combustion liner from the turbine with attendant removal of certain piping for fuel, as well as piping for oil and water systems and auxiliary air piping for atomization. It is also necessary to remove the heavy end cover of the combustor to gain access to the dilution holes. Further, there is the possibility of contaminating the fuel system in the process of removing and reassembling the various piping systems. The combustion liners are then sent to a service shop to have the existing dilution holes resized. Still further, this process can take between one to two weeks time, during which there is a gas turbine outage, preventing the electricity provider from producing power during that period of time. Consequently, there is a need for a system that facilitates change of the combustor dilution hole areas without disassembly and subsequent reassembly of major portions of the combustor and in a reduced timeframe.
In accordance with an embodiment of the present invention, there is provided a mechanical arrangement enabling external access to the combustion chamber which facilitates changeover of combustor dilution hole areas to adjust the NOX levels without disassembly of the combustors. To accomplish this, the combustion liner and surrounding air flow sleeve have aligned radial openings at an axial location along the liner for admitting dilution air through dilution sleeves in the aligned radial openings into the combustion chamber. An outer casing surrounds the flow sleeve and defines with the flow sleeve an annular flow passage for flowing compressor discharge air through the dilution sleeves into the combustion chamber. The openings through the flow sleeve are provided with collars which form seats for receiving flanges of the dilution sleeves. The outer casing is also provided with a cylindrical boss or flange in line with the axes of the openings through the combustion liner and flow sleeve, affording access to the dilution sleeves externally of the combustor. A cover is releasably secured to the cylindrical flange, for example, by bolts, and a spring cooperates between the cover and the flange on each dilution sleeve to maintain the dilution sleeve in the aligned openings of the combustion liner and flow sleeve with the flange of the dilution sleeve seated on the collar.
Each dilution sleeve has a central opening of a predetermined area. In the event that the NOX emissions are out of compliance after initial installation of the gas turbine, the access covers to the installed dilution sleeves are removed and dilution sleeves having holes of different areas are inserted to provide more or less compressor discharge air flow through the sleeves into the combustion chamber. Particularly, after the NOX emissions of the newly installed turbine have been measured at the design operating conditions, the actual measured NOX emission level is compared with the required NOX emission level for compliance. If the measured NOX emissions deviate to the extent the turbine is out of compliance, an increase or decrease in the hole area of the installed dilution sleeves is calculated to arrive at a dilution hole area effective to provide a NOX emission level within the compliance range. Once the required dilution hole area is determined, the combustion covers are removed and a new set of dilution sleeves conforming to the new required hole area is provided. Alternatively, the initially installed set of dilution sleeves are machined to the required new dilution hole areas. In either case, the dilution sleeves with the required hole areas are inserted through the cylindrical bosses to seat on the collars about the openings in the flow sleeve and extend through the aligned openings through the flow sleeve and the combustion liner. The springs and covers are then reinstalled to secure the dilution sleeves in place with the properly sized dilution hole areas.
In an embodiment according to the present invention, there is provided a combustor for a gas turbine comprising an outer casing, a flow sleeve within the outer casing defining an air flow passage with the outer casing, a combustion liner within the flow sleeve for flowing hot gases of combustion, at least one opening in each combustion liner and the flow sleeve, a dilution sleeve removably received within the openings of the combustion liner and the flow sleeve and an access port in the outer casing for access to the dilution sleeve, the dilution sleeve being sized for passage through the access port enabling insertion into or removal of the dilution sleeve from the openings.
In a further embodiment according to the present invention, there is provided in a combustor for a gas turbine having a combustion liner defining a hot gas flow path, an outer casing, a flow sleeve between the outer casing and the liner defining a dilution air flow path therebetween, and openings through the flow sleeve and the liner for flowing dilution air in the dilution air flow path into the hot gas flow path, a method of adjusting the level of NOX emissions comprising the steps of (a) providing a dilution air flow sleeve in the openings having an air flow passage of a predetermined area, (b) measuring the NOX emissions from the gas turbine at design operating conditions, (c) determining a deviation of the measured NOX emissions from a predetermined desired level of NOX emissions, (d) ascertaining a predetermined area of a desired air flow passage through an air flow dilution sleeve based on the deviation, and (e) installing an air flow dilution sleeve in the turbine having a flow area sized to provide at least approximately the desired level of NOX emissions.
An alternative embodiment of the present invention comprises a combustor air tuning liner design having combustor orifice assembly comprising a boss, an orifice plate, and a retaining ring. This embodiment provides an alternative construction for the retuning of a combustor by allowing for the replacement of incorrectly sized orifices with correctly sized orifices, all without having to send the combustion liner to a service shop. Thus, the alternative embodiment of the present invention reduces the time and money needed retune combustors to achieve a desired level of NOX emissions.
Further, since the only part that is replaced is the orifice plate, the present invention provides for easy and efficient retuning than a retune that requires service shop work on the combustion liner. This alternative embodiment can be used to retune a combustor prior to or after the combustor is placed into service so that it meets emission requirements.
The present invention eliminates service shop time and cost, and at the same time provides operator friendly dilution hole change capability. Further, the present invention provides proper cooling for successful operation in a harsh thermal environment where the liner skin reaches about greater than 1400 degrees Fahrenheit. In addition, the present invention provides a simple, reliable, and structurally sound design.